1. Field of the Invention
The present invention relates to the automatic display and interpretation of the operations of a ferrous debris detector of the type which generates pulses of electricity to disintegrate magnetically concentrated accumulations of 0 to 10 micron sized wear particles in hydraulic systems.
2. Description of the Prior Art
One characteristic of heavily loaded mechanical systems, such as helicopter transmissions and rotor gear boxed which are lubricated by pressurized circulating oil streams, is the generation of some quantity 0 -10 micron sized particles by the constitutent parts as they wear in service. The particles of "fuzz" are picked up and circulate throughout the oil system with pumped oil. In addition where system overloads which lead to chipping of mating parts, such as gear teeth, or excessive vibration leading to the initiation of fatigue cracks occur, larger particles, having diameters of 100 microns will start to appear. If these conditions are allowed to progress without being detected and checked, catastrophic failure may result in service.
There exist today a large number of devices for the purpose of removing and analyzing potentially harmful debris particles from pressurized hydraulic systems. These may be filtering devices for varying complexity such as that shown by Miller and Rumberger in U.S. Pat. No. 3,878,103 or cyclonic devices shown as those shown by Schulze in U.S. Pat. No. 3,129,173 and Martin in U.S. Pat. No. 3,528,552. Where ferrous particles are involved such devices often include a magnet to aid in attracting and capturingthese particles. A wide variety of such devices exist ranging from fairly simple units similar to that shown by Botstiber in U.S. Pat. No. 2,936,890 to more complex combination filter and magnet systems such as those shown by Botstiber in U.S. Pat. No. 3,317,042, Winslow in U.S. Pat. No. 3,127,255, Patton in U.S. Pat. No. 2,980,257 and Lammers in U.S. Pat. No. 3,421,627.
Many of these devices provide a dynamic, positive means for monitoring system status by signalling the arrival and capture of one or more particles. Such signalling systems are shown by Botstiber in U.S. Pat. Nos. 3,432,750 and 3,317,042, Booth in U.S. Pat. No. 2,462,715 and Bourne in U.S. Pat. No. 2,450,630. These systems have found wide use in many types of helicopter engines and transmission systems. It should be noted, however, that in most applications it is usually felt to be unnecessary to announce the capture of individual fuzz particles since there are, relatively speaking, quite a large number of them. Also their small size makes them comparatively innocuous as long as they are freely moving in the system. Therefore, a regularly scheduled cleanup of the magnet is about all that is normally needed when fuzz is the only contaminent present.
On the other hand, if particles in excess of 100 microns start to appear it is most important that the pilot or operator be altered to each of them as they arrive since the number of such particles captured and their rate of arrival will provide an early warning of cracking or impending fatigue failure somewhere in the system. When these events occur, accelerated maintenance must be scheduled to find and repair the affected areas if catastrophic failure is to be avoided. This signal discrimination is normally done by using either an insulated screen type filter or a electric chip detector which is connected to an alarm. It is only when the wires in the screen or the magnet poles are bridged by "large" particles that the alarm will sound. The pole gap or screen openings are, in theory, large enough for fuzz particles to pass through and therefore not trigger the alarm. In practice, however, it is sometimes found that particles of fuzz will also tend to collect around the openings and agglomerate to the point where they too will bridge them and generate an alarm. In most state-of-the-art devices there is usually no way short of stopping the engine and visually examining the detector to determine if such an alarm is spurious or not. While spurious signals do not require a more extensive tear down inspection, as would a real one, they obviously tend to seriously impede the efficient, continuing use of the system.
There is available today one type of detector system which attempts to prevent this problem. In this system, which is described by Tauber in U.S. Pat. No. 4,070,660, the material bridging the gap is subjected to a pulse of current. This acts to disintegrate fuzz agglomerates and break the electrical alarm circuitwhile leaving large particles and therefore the alarm circuit unaffected. Such a system has been found to be quite successful in reducing the number of unscheduled maintenance operations. However, as experience has been gained with this type of detector it has been found that a knowledge of fuzz buildup can often provide valuable information as to the degree and nature of the wear being experienced by the hydraulic system and the components operating in it. Thus, in a properly aligned and loaded gear train, for example, a specific rate and pattern of wear particle generation, defined more or less as "normal", can be expected. Where there are problems with improper alignments or system overloads, or where gears and other mating parts show defects, one would then expect to find non-specific or "abnormal" particle generation rates and patterns. It has been found that in a pulse type of system, as described above, keeping track of the number and/or rate of "successful" discharges can provide useful data as to rate and pattern "normality". Thus, when either a predetermined number of discharges is reached or rate/unit time exceeds a predetermined level an appropriate alarm can be sounded to call attention to the problem. By so doing proper maintenance can be scheduled without having to unnecessarily abort the operation of the system.